diff --git a/attribute/coords.go b/attribute/coords.go
index 6acfff1..5c425e8 100644
--- a/attribute/coords.go
+++ b/attribute/coords.go
@@ -1,19 +1,27 @@
 package attribute
 
 import (
-	"strconv"
-	"strings"
+	"bytes"
 
 	"gitlab.codemonkeysoftware.net/b/hatmill"
 )
 
-func Coords(values ...float32) hatmill.Attrib {
-	s := make([]string, 0, len(values))
-	for _, value := range values {
-		s = append(s, strconv.FormatFloat(float64(value), 'G', -1, 32))
+type CoordsList []float32
+
+func (l CoordsList) String() string {
+	var buf bytes.Buffer
+	for i, f := range l {
+		if i > 0 {
+			buf.WriteRune(',')
+		}
+		buf.WriteString(Float(f).String())
 	}
+	return buf.String()
+}
+
+func Coords(values ...float32) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "coords",
-		Value: String(strings.Join(s, ",")),
+		Value: CoordsList(values),
 	}
 }
diff --git a/attribute/coords_test.go b/attribute/coords_test.go
index d38b7cf..80f96fb 100644
--- a/attribute/coords_test.go
+++ b/attribute/coords_test.go
@@ -6,35 +6,35 @@ import (
 	"gitlab.codemonkeysoftware.net/b/hatmill/attribute"
 )
 
-func TestCoordsNumberFormat(t *testing.T) {
-	for _, testcase := range []struct {
-		name  string
-		f     float32
-		value string
-	}{
-		{name: "zero", f: 0, value: "0"},
-		{name: "integral", f: 45, value: "45"},
-		{name: "positive fractional, small positive exponent", f: 12.55, value: "12.55"},
-		{name: "positive fractional, large positive exponent", f: 1.55E+12, value: "1.55E+12"},
-		{name: "positive fractional, large negative exponent", f: 1.55E-12, value: "1.55E-12"},
-		{name: "negative fractional, small positive exponent", f: -12.55, value: "-12.55"},
-		{name: "negative fractional, large positive exponent", f: -1.55E+12, value: "-1.55E+12"},
-		{name: "negative fractional, large negative exponent", f: -1.55E-12, value: "-1.55E-12"},
-	} {
-		t.Run(testcase.name, func(t *testing.T) {
-			testAttribValue(t, attribute.Coords(testcase.f), testcase.value)
-		})
-	}
-}
+func TestCoordsList(t *testing.T) {
+	t.Run("String returns empty string for empty list", func(t *testing.T) {
+		expectEqualStrings(t, attribute.CoordsList(nil).String(), "")
+	})
 
-func TestCoordsCardinality(t *testing.T) {
-	t.Run("zero", func(t *testing.T) {
-		testAttribValue(t, attribute.Coords(), "")
+	t.Run("String uses valid number format", func(t *testing.T) {
+		for _, testcase := range []struct {
+			name string
+			f    float32
+			s    string
+		}{
+			{name: "zero", f: 0, s: "0"},
+			{name: "integral", f: 45, s: "45"},
+			{name: "positive fractional, small positive exponent", f: 12.55, s: "12.55"},
+			{name: "positive fractional, large positive exponent", f: 1.55E+12, s: "1.55E+12"},
+			{name: "positive fractional, large negative exponent", f: 1.55E-12, s: "1.55E-12"},
+			{name: "negative fractional, small positive exponent", f: -12.55, s: "-12.55"},
+			{name: "negative fractional, large positive exponent", f: -1.55E+12, s: "-1.55E+12"},
+			{name: "negative fractional, large negative exponent", f: -1.55E-12, s: "-1.55E-12"},
+		} {
+			t.Run(testcase.name, func(t *testing.T) {
+				expectEqualStrings(t, attribute.CoordsList{testcase.f}.String(), testcase.s)
+			})
+		}
 	})
-	t.Run("one", func(t *testing.T) {
-		testAttribValue(t, attribute.Coords(5), "5")
-	})
-	t.Run("many", func(t *testing.T) {
-		testAttribValue(t, attribute.Coords(5, 4, 3, 2, 1), "5,4,3,2,1")
+
+	t.Run("String inserts delimiter in lists with length > 1", func(t *testing.T) {
+		actual := attribute.CoordsList{0, 0}.String()
+		expected := "0,0"
+		expectEqualStrings(t, actual, expected)
 	})
 }